Golf club head

ABSTRACT

A golf club head of this invention includes a face, a plurality of score line grooves formed on the face, and a plurality of striations formed on the face. The angle formed by an arrangement direction of the plurality of striations and the score line grooves is between 40 degrees and 70 degrees, inclusive, as viewed clockwise from a toe side end of the score line grooves.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf club head.

2. Description of the Related Art

The face of a golf club head include a plurality of grooves, known asmarking lines, score lines, or face line grooves (hereinafter referredto as score line grooves), which affect the spin amount on a ball. It isdesirable to have the grooves on an iron club head, especially a wedge,in order to increase the spin amount on the ball. The surface roughnessof the face also influences the spin amount of a ball. Japanese PatentNo. 3,000,921 discloses a golf club head in which a plurality of finegrooves are formed on the face in addition to the score line grooves.

A wedge gold club head such as a sand wedge or approach wedge is usedwith the face perpendicular to a target direction, with the face open,or with the face closed. For example, when a player wants to hit a ballhigh, he or she generally uses the golf club with the face open. Whenthe player wants to roll a ball, he or she generally uses the golf clubwith the face closed. When the face is directed perpendicularly to thetarget direction or is open, the larger spin amount of the ball isdesirable, and particularly when the face is open, the large spin amountof the ball is desirable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a golf club headwhich can obtain the larger spin amount of a ball.

According to the present invention, there is provided a golf club headcomprising a face, a plurality of score line grooves formed on the face,and, a plurality of striations formed on the face, wherein an angleformed by an arrangement direction of the plurality of striations andthe score line grooves is between 40 degrees and 70 degrees, inclusive,as viewed clockwise from a toe side end of the score line grooves.

In the golf club head of the present invention, since the plurality ofstriations are formed, the friction force between the ball and the facecan increase and the larger spin amount of the ball can be obtained. Inaddition, the angle between the arrangement direction of the pluralityof striations and the score line grooves is between 40 degrees and 70degrees, inclusive, as viewed clockwise from a toe side end of the scoreline grooves. With this arrangement, when the golf club is used with theface open, spin can be easily imparted to the ball, and the larger spinamount can be obtained.

According to the present invention, there is provided a golf club headcomprising, a face, and a plurality of striations formed on the face,wherein when the golf club head is placed on a horizontal plane at adefined lie angle and a defined loft angle, an angle formed by anarrangement direction of the plurality of striations and a horizontaldirection parallel to the face is between 40 degrees and 70 degrees,inclusive, as viewed clockwise from a toe side end of the golf clubhead.

In the golf club head of the present invention, since the plurality ofstriations are formed, the friction force between the ball and the facecan increase and the larger spin amount of the ball can be obtained. Inaddition, the angle between the arrangement direction of the pluralityof striations and a horizontal direction parallel to the face is between40 degrees and 70 degrees, inclusive, as viewed clockwise from a toeside end of the golf club head. With this arrangement, when the golfclub is used with the face open, spin can be easily imparted to theball, and the larger spin amount can be obtained.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of a golf club head A, according to anembodiment of the present invention.

FIG. 2 is a cross-sectional diagram in the vicinity of a score linegrooves 20, which cuts at right angles to the lengthwise, or toe-heeldirection, of the score line grooves.

FIG. 3 shows views illustrating a forming method of striations 30 usinga milling machine.

FIG. 4 is a plan view showing a moving path of a cutting tool 1 whenmilling the striations 30 by milling.

FIG. 5A depicts a face 10 when directly facing in the target direction.

FIG. 5B depicts the face 10 when opened.

FIG. 6 is a view showing the outer appearance of a golf club head Baccording another embodiment of the present invention.

FIG. 7 is a table showing the test results obtained by measuring thespin amount of the ball for Examples 1 and 2 according to the presentinvention and Comparative Examples 1 to 7;

FIG. 8A is a graph showing the “spin amount”-“Ra” relationship of thetest results shown in FIG. 7;

FIG. 8B is a graph showing the “spin amount”-“θ0” relationship of thetest results shown in FIG. 7; and

FIG. 9 is a view for explaining another definition method of an angleθ0.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is an external view of a golf club head A, according to anembodiment of the present invention. The embodiment depicted in FIG. 1applies the present invention to an iron club head. The presentinvention is optimized for club heads for which large spin amount isrequired, especially wedges such as sand wedges, pitching wedges, orapproach wedges. The present invention may also be applied to golf clubhead for the wood type or the utility type.

The face 10 of the golf club head A comprises a plurality of the scoreline grooves 20. The face 10 is the surface that strikes the golf ball.According to the embodiment, the respective score line grooves 20 arearrayed in straight lines in the toe-heel direction, all in parallel,with equal pitch between the respective score line grooves 20.

FIG. 2 is a cross-sectional diagram in the vicinity of a score linegrooves 20, which cuts at right angles to the lengthwise, or toe-heeldirection, of the score line grooves. In the embodiment, thecross-section of each score line groove 20 is constant in the lengthwisedirection, except at the ends. The score line grooves 20 have the sametrapezoidal sectional shape.

Referring to FIGS. 1 and 2, a plurality of striations 30 are formed onthe face 10. Each striation 30 is of a significantly small formaccording to the embodiment, being smaller in cross section area thanthe score line groove 20. In the embodiment, each striation 30 forms acircular arc, and is shaped so as not to overlap any other striation 30.Also in the embodiment, each striation 30 is an arc of radius identicalto every other striation 30.

An arrow d0 in FIG. 1 depicts an arrangement direction of the pluralityof striations 30. In the embodiment, each striation 30 is an arc ofradius identical to every other striation 30 as described above. Thearrangement direction d0 is defined as the direction that passes throughthe center of the circle of arc of each striation 30. An angle θ0, whichis formed by the arrangement direction d0 and the lengthwise directionof the score line groove 20, is between 40 and 70 degrees, inclusive, asmeasured clockwise from the toe side end of the score line groove 20.With regard to the striations 30 depicted in FIG. 1, the angle θ0 isapproximately 45 degrees.

The angle θ0 can be defined by using a method other than therelationship between the arrangement direction d0 and the score linegroove 20. FIG. 9 is a view for explaining another definition method ofthe angle θ0. In the example shown in FIG. 9, the angle θ0 is defined asan angle between the arrangement direction d0 of the striations and ahorizontal direction HL parallel to the face when the golf club head isplaced on a horizontal plane HS at the defined lie angle and loft angle.

In the example shown in FIG. 9, the angle θ0 is also 40° to 70° (bothinclusive) in the clockwise direction from the toe side end of the golfclub head. The definition method of the angle θ0 of the example shown inFIG. 9 can be used, for example, when the arrangement direction of thestriations is defined in a golf club head in which no score line grooveor irregular score line grooves are formed.

The striations 30 can be formed as traces by milling. Milling can beperformed using, e.g., a milling machine. FIG. 3 is a schematic diagramillustrative of a forming method of striations 30 using a millingmachine. The milling machine comprises a spindle 2 that rotates about avertical axis Z, and a cutting tool (endmill) 1 is attached to the lowerend of the spindle 2. A golf club head A, that has not been formed withthe striations 30, fixed with the milling machine by way of a jig 3 sothat the face 10 is horizontal. A cutting portion 1 a of the cuttingtool is separated from the vertical axis Z by a distance rt, which isthe radius of the circle of arc of each striation 30.

FIG. 4 is a planar view diagram illustrative of a moving path of thecutting tool 1 when milling the striations 30. The relative direction ofmovement, i.e., the horizontal direction, of the cutting tool 1 and thegolf club head A, is identical with the arrangement direction d0 of thestriations 30. As the cutting tool 1 is moved in the arrangementdirection d0, relative to the golf club head A, the plurality ofstriations 30 is formed by milling the face 10 with the cutting tool 1.The center of the circle arc of each striation 30, or in other words,the position of the vertical axis Z, passes through the arrangementdirection d0. Accordingly, the arrangement direction d0 is the directionthat passes through the center of the circle arc of each striation 30.The depth, width, and pitch of each striation 30 is adjusted by thedepth of the cut into the face 10 by the cutting tool 1 and the relativemoving speed of the cutting tool 1.

The effect of the striations 30 will be described next. In thisembodiment, since the plurality of the striations 30 are formed, thesurface roughness increases as compared to a case wherein the face 10 isplanished. When the surface roughness of the face 10 increases, thefriction force between the ball and face 10 increases, and spin can beeasily imparted to the ball. As the surface roughness of the face 10increases, more spin is imparted to the ball. In this case, however, theball is easily damaged.

Accordingly, it is preferable for the surface roughness of the portionof the face 10 that forms the striations 30 to have the arithmetic meandeviation of the profile (Ra) of between 4.00 μm and 4.57 μm, inclusive.It is also preferable for the maximum height of the profile (Ry) to benot greater than 25 μm. Keeping the surface roughness of the face 10within the specified range of values also meets the regulationspertaining to the surface roughness of the face of a golf club head tobe used in official competition golf.

Next, in the embodiment, since the angle θ0, which is formed from thearrangement direction d0 of the plurality of striations 30 and the scoreline groove 20, is between 40 degrees and 70 degrees, inclusive, itbecomes easier to impart spin to the ball, allowing obtaining a greaterspin amount when using a golf club with the golf club head A when theface 10 is opened, as described in FIGS. 5A and 5B.

FIG. 5A depicts a situation wherein the face 10 is facing directly inthe target direction, and FIG. 5B depicts a situation wherein the face10 is opened. The striations 30 have been omitted from FIGS. 5A and 5B.The arrows in FIGS. 5A and 5B depict the direction of relative movementof the ball vis-a-vis the face 10 at time of impact.

In the embodiment, applying the plurality of striations 30 makes iteasier to impart spin to the ball in both the situation shown in FIG. 5Aand FIG. 5B. If the face 10 is opened, as depicted in FIG. 5B, resultsin the ball rubbing against the face 10 at time of impact in such amanner as to intersect the score line grooves 20 at an angle.

Presuming the angle θ0, which is formed by the arrangement direction d0of the plurality of the striations 30 and the score line grooves 20, tobe between 40 and 70 degrees, according to the embodiment, the number ofstriations 30 that rub against the ball is increased when the face 10 isopened, as depicted in FIG. 5B. To put it another way, the angle of thedirection of relative movement of the ball and the striations 30approaches a right angle. Accordingly, it becomes easier to impart spinto the ball, allowing obtaining a greater spin amount.

While each striation 30 has been formed as a circular arc according tothe embodiment, it is possible to form the striations 30 as a straightline as well. FIG. 6 is an external view of an example of a golf clubhead B with striations in a different shape. The golf club head B isidentical to the golf club head A, except for the fact that a pluralityof striations 40 are formed of straight lines.

The plurality of striations 40 are mutually formed in parallel. Wheneach striation 40 is straight lines, according to the embodiment, anarrangement direction d0′ is defined as a direction that is orthogonalto each striation 40. An angle θ0′ formed from the arrangement directiond0′ and the lengthwise direction of the score line groove 20 is between40 and 70 degrees, inclusive, as measured clockwise from the toe sideend of the score line groove 20.

Even if the striations 40 have a straight line shape, it is easier toimpart spin to the ball, and it is particularly easier to impart spin tothe ball when the face 10 is opened, making it easier to obtain agreater spin amount on the ball in either case.

EXAMPLES

FIG. 7 is a table showing the test results obtained by measuring thespin amount of the ball for Examples 1 and 2 according to the presentinvention and Comparative Examples 1 to 7. All of Examples 1 and 2 andComparative Examples 1 to 7 are sand wedges with a loft angle of 56°using golf club heads with the circular arc striations 30 shown inFIG. 1. For all of Examples 1 and 2 and Comparative Examples 1 to 7, acutting tool with a radius (rt in FIG. 3) of 37.5 mm was used to formthe striations 30 by milling.

The “θ0” in FIG. 7 is the θ0 depicted in FIG. 1, an angle formed by anarrangement direction of the striations 30, i.e., the d0 in FIG. 1, andthe score line groove. The “Ra” is actual measured value of thearithmetic mean deviation of the profile on the face in which thestriations are formed.

The “spin amount” in FIG. 7 depicts the spin amount on the ball. Thespin amount is calculated by marking the ball prior to the shot, andusing a video camera to track the change in the location of the mark attime of impact.

The test involved using golf clubs of Examples 1 and 2 and ComparativeExamples 1 to 7, and having three testers hit a golf ball out of therough, aiming at a target 40 yards away. The three testers hit fiveballs with the face in direct line with the target direction, and fiveballs with the face opened. The angle at which the face was opened wasleft up to the testers' discretion.

The “normal”, under the spin amount heading in FIG. 7, is the averagevalue of the amount of spin when the face is in direct line with thetarget direction, and the “open” is the average value of the spin amountwhen the face is opened.

FIG. 8A graphs the relationship between the spin amount and the Raexperimental findings depicted in FIG. 7. It is apparent that therougher the face, the more spin on the ball, for both the normal and theopen circumstance. The slope of the plot becomes steeper near the pointwhere Ra reaches 4 μm, which suggests that the Ra of not less than 4 μmis preferable. Taking into account such factors as the fact that therougher the face, the easier it is to damage the ball, as well asregulations pertaining to the surface roughness of the face on golf clubheads that are used in official competition play, suggests that thearithmetic mean deviation of the profile Ra on the face of between 4.00μm and 4.57 μm, inclusive, is preferable.

FIG. 8B graphs the relationship between the spin amount and the θ0experimental findings depicted in FIG. 7 for Example 1 and 2 andComparative Examples 5 to 7, all of which have identical surfaceroughness on the face, i.e., Ra: 4.4 μm.

It is apparent that the spin amount increases as the θ0 ranges from 0 tothe vicinity of 55 degrees, and then declines as the θ0 exceeds 55degrees, for both the normal and the open circumstance. For the range ofθ0 between approximately 30 and 80 degrees, centering on the vicinity of55 degrees, an spin amount of 7000 rpm or more may be obtained in theopen circumstance, which suggests that a sufficient spin amount may beobtained in the open circumstance when the θ0 is between 40 and 70degrees, inclusive.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-320750, filed Nov. 28, 2006, which is hereby incorporated byreference herein in its entirety.

1. A golf club head comprising: a face; a plurality of score linegrooves formed on the face; and a plurality of striations formed on theface, wherein an angle formed by an arrangement direction of theplurality of striations and said score line grooves is between 40degrees and 70 degrees, inclusive, as viewed clockwise from a toe sideend of said score line grooves.
 2. The golf club head according to claim1, wherein each striation forms a circular arc, and the arrangementdirection is a direction that intersects the center of the circular arcof each striation.
 3. The golf club head according to claim 2, whereinthe plurality of striations are formed by milling.
 4. The golf club headaccording to claim 1, wherein said face in which the striations areformed has the arithmetic mean deviation of the profile (Ra) of not lessthan 4.00 μm and not more than 4.57 μm.
 5. A golf club head comprising:a face; and a plurality of striations formed on the face, wherein whenthe golf club head is placed on a horizontal plane at a defined lieangle and a defined loft angle, an angle formed by an arrangementdirection of the plurality of striations and a horizontal directionparallel to the face is between 40 degrees and 70 degrees, inclusive, asviewed clockwise from a toe side end of said golf club head.